Method for the purification of zinc soluticns



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CQBELL, OF DENVER, CQLR'G.

This invention relates to a method for the purififutieu of zinc solutions.

Methods now in use consist, usually, of ille 'following stepst-{o} neutralization and oxiilalion to remove iron, and (il) precipitation. o' Cin Cd, on zinc dust or scrap. Other steps are sometimes added for the more complete removal of (lo, lli, etc. when this is necessary.

l/Vhere an ammoniacal solution is employedj iron is not readily soluble, and in :uch cases it is only' 'necessary lo precipitate the Cu, Cd, etc. on zinc.

Vin cases where either acid or alkali solulions are enniloyed, 'the removal ol Cu and Cd is of prime importance. This is attended by many diiiculties. lfrecipitsted Cu and Cfl-- :pccinlly the latter-Wham a tendency lo oxidiL/.e in the presence of air, fe od il' this occurs, the. oxides lend to go back Anto solution, precipitating the Zinc as Zn() or loi `.ij basic salts ol zinc. Once oxidation of s type in, itbecomcs very dilhcult to remore the Cu and Cd.

in different plants, air and mechanical u itetors ure ci'nployed lor bringing about precipitation on zinc, lllliere air is eln- ;1 l yo 'l there is a marked tendency towards oxidation and a consecucnt. increase in the amount ol zine required. l,libere mechanirul means :ire employed to produce the ne sary agitation, the tendency towards oxidation is less marked and decreases in proportion. as the Contact with air is prevented.

gitaion, however effecten7 must be followed by settlingT and filtering orby iltra tion alone, usually 'in .filter presses, so as to clarify the solution. Tl ese operations are costly both as the equipment necessary and the labor which they entail, and, besides this. they olier further chances 'for oxidation.

lt is evident that the use of agitators is objectionable and that it is highly desirable to obtain the desired results by means that do not employ agitation.

i have found if an impure solution a :aine salt is allowed to percoiate u ward ly through a tower filled with loose y packed zinc slm-t, the Cn and Cd will be removed to an sullcienl; to insure suecess'ul electro-deposition of the zinc. 'Where a simple tower is employed the precipitated metals are carried over with the elluent liquors which tlierefore require subsequently to be Filtered.

ln order to obviate the last-named diiliculty, have invented an apparatusI which l will now describe in detail, reference for this purpose being had to the accompanying drawing where the single View shows a vertical diametrical section through the apparatus.

lily apparatus or tower consists of a metal cylinder 5 of any suitable size and may be about live lect in length and three feet in diameter. The lower end of this cylinder is closed by means of s conical cover 6, while the upper end thereof is closed by a convex or spherical @over member 7. Secured to the inside of the cylinder near its lower end is a metal screen 8 having about four meshes lo he inch. A cylindrical member or tube 9 extends upwardly centrally of the cylinder. The lower end of this tube opens outwardly through the side of the conical member 6, as indicated by numeral 10 and has its upper end at or about the level ol the upper end of the cylinder 5. The member 9 is enclosed by a conical casing ll which rests on the screen 8 or on suitable supports adjacent to the screen. The cylinder 5 is provided near its upper end with an outlet l2. lt will be notie/ed that the chamber formed by the cylinder 5 and the. ends 6 and 7 is divided into four compartments by the screen 8 and members 9 and il. These compartments have been designated by letters A, B, C, and D. Compertments A and B are completely Filled with zinc shot scrap, turnings, etc., and compartment C is partially illed.

For use with ammoniacal solutions, the tower may be made of cast-iron or steel, but where acid solutions, such as Z'nSQL are used, the iron, if used, must be lead lined. ln the latter case other non-corrosive material such as wood is preferable.

The impure solutions enter at 10 and flow upwardly through the central compartment A, thence. downwardly 'through the compartment B and upwardly through compartment C, thence out through 1Q'. As the crosssectionsl area o mpertments A B and C increases in the or-der given, the solutions will. have the highest velocity in compart ment A Where the rate of reaction is the greatest. It is essential that the velocity in compartment A shall be quite high, as the precipitated metals must be swept from the surfaces of the zinc shot by means of the upward movement of the solution.

The velocity of flow in compartment B is less than in compartment. A and decreases towards the bottom as the area increases, but must be sufficiently great to prevent clogging and to carry the precipitated metals through the supporting screen S into the compartment D. The increased area of compartment C causes the velocity to be decreased to such an extent that settling takes place. The method should be so carried out that the precipitation willbe completed in the compartment B and therefore only enough zinc is placed in C to prevent contamination due to slimes carried up from D. Where a large capacity is required, it may be desirable to use two such towers in series, as I have found. owing to the much greater velocities that may be maintained, two towers in series will have. a capacity of more than three times that of a single tower. The use of high velocities is desirable, as clogging is not noticed while there is a constant tendency to clog at low velocities.

The recipitated metals and sludge are collecte in compartment D, from which they may be removed through the manhole 13, or they may be taken out continuously by means of, say, a drain inserted in the bottom of the cover 6. If it should be found desirable to-recover the Cu and Cd following formula After the solution has passed through the first tower or sets of towers, it is then passed through the second tower oi` sets of towers where separation takes place in accordance with the following formula that required by the above equations; but 79 in any (usr the exact amount. to be added must be lettl to the discretion= of the operator.

TheA top of the tower is provided with a dome l-t having an opening l5 through l5 which the generated gases may escape.

The apparatus shown and described is illustrative only and the method may be carried out by means that are specifically different than that shown, .but which are the equivalent for the purpose.

Having now described my invention, what I claim as new isr- 1. The method for the purification of zine solutions, which consists in causing the solu- 99 -tion to percolate successively through separate compartments containing loosely packed particles of metallic zinc, each successive compartment being of greater area whereby the velocity of the solution de- 9@ PTQHSGS.

2. The method for the` purification of zinc salt solutions containing salts of more negative metals which consists in causing lthe `solutionto 'percolatc upwardly through",135

a compartment containing loosely packed particles of metallic zinc, thence down` wardly through a second com artment of larger transverse area which a so contains metallic zinc particles, thence upwardly Nt@ through a. third compartment of still lgreater area, which contains loosely packed particles ot metallic zinc.

3. The method of purification of impure zinc solutions, which consists in causing the im solution to pei-colate at decreasing velocities through separate compartments containing loosely packed metallic zinc articles.

4. The method of purification of impure zinc solutions,.which consists in causing the El@ solution `to percolate upwardly through a mass of loosely packed zinc particles at a velocitffsutiiciently great to carry along the precipitated metals, then causing the soiution to percolatc downwardly through a IMS second compartment containing loosely packed particles of metallic zinc, the velocity of .flow through the second comparb ment being less than in the first compartment, but suiiciently great to prevent clogilv 'ging 'and then passing the solution through a third com artment at a velocity which permlts'setthng to take place.

5. The method of purification of impure zinc solutions, which consists in causing the mi solution to percolate upwardly through a mass of loosely packed zinc particles at a velocit-y sufficiently great to carry along the precipitated metals, then causing the solution to percolate downwardly through a iso mamas through he last compa'tmem being ezf' that settling will take place.

In testimony whereof tu'e. 

